Selvig is an astrophysicist, I don't see him being the one involved. The most likely candidate is Tony as he is the only one shown capable of creating A.I., and the fact that he used to be a weapons manufacturer.

I'm guessing that at one time, Tony had created the project, the government scrapped it, and he took what he had to create Jarvis, based off loving memory of his father's butler growing up. The government stole the plans from Stark and continued their work, and then Ultron was born.

__________________"If you step out that door, you're an Avenger" - Hawkeye